1. Field of Invention
This invention relates to the field of lawnmowers and, more specifically, to zero turn lawnmowers and a mechanical control lever and parking brake interlock for such mowers.
2. Description of Related Art
It is known in the art to provide vehicles such as lawnmowers with drive systems that provide for Zero Turn Radius (ZTR) steering. ZTR vehicles typically have two drive wheels that can be rotated at different speeds to achieve turning. The drive wheels can also be rotated in different directions for a very sharp turn or even a zero turn radius which is when the mower actually turns about the mid point of the drive wheel axis. The other wheels on the mower are castered and merely follow the drive wheels.
ZTR vehicles are typically controlled by a pair of side-by-side speed control levers that are independently operated for use in steering and propelling the vehicle. The speed control levers move forward and aft from a neutral position to achieve variable speed and steering. These two essentially vertically positioned levers can be positioned close together between the operator's knees or positioned out to the sides of the operator with horizontal gripping portions extending in toward the center of the mower for easy side-by-side gripping. Each of the dual speed control levers are connected to a respective drive device, such as a hydrostatic drive, that are, in turn, connected to the drive wheels for use in propelling and steering the vehicle. The hydrostatic drive typically includes a variable displacement axial piston hydraulic pump for each of the two fixed axle drive wheels. Each speed control lever independently controls the speed of one of the drive wheels which permits a variety of maneuvers including rotating one wheel forward while rotating the other backward, which causes the mower to turn within its own dimensions. With ZTR steering, the vehicle becomes much more maneuverable than conventional vehicle steering.
ZTR vehicles typically require means to prevent starting the machine unless the control levers are in their neutral positions. This is typically accomplished by sensing the position of the speed control levers and disabling the starting control power circuit unless the speed control levers are in their neutral position. Thus, the operator is typically required to place the speed control levers into slotted sections corresponding to the neutral position of the levers to activate the neutral position switches. Other systems have intricate mechanical systems that force the speed control levers into the neutral position when the parking brake is set. Such prior arrangements are complicated and expensive to manufacture and yet not totally reliable.